dynamic stretching vs. foam rolling: effects on hamstring flexibility and muscle oxygenation in tight hamstrings

Conditions: Hamstring Contractures; Muscle Relaxation; Muscle Tightness

Summary: hamstring flexibility plays a vital role in functional movement and injury prevention. decreased flexibility is common and can lead to biomechanical dysfunctions, limited range of motion, and poor posture. interventions like stretching exercises and myofascial release are widely used to improve muscle flexibility. dynamic stretching (ds) involves active muscle movements and has been shown to significantly enhance flexibility, potentially more effectively than static stretching (ss). foam rolling (fr), a self-myofascial release technique, also improves flexibility and may offer additional benefits by increasing fascial mobility without impairing strength. peripheral muscle oxygenation (smo₂) reflects a muscle's ability to use oxygen and is increasingly used to assess performance and fatigue. though studies suggest that stretching and fr may improve smo₂, evidence remains limited. this study aimed to compare the effects of isolated, single-session ds and fr on hamstring flexibility and muscle oxygenation. the hypothesis proposed that ds would be more effective than fr in enhancing muscle oxygenation, while both would similarly improve flexibility.

muscle flexibility is defined as the capacity of muscle tissue to elongate and is considered one of the key components in maintaining physical fitness. the hamstring muscles are primarily responsible for knee flexion and play a crucial role in the proper execution of functional activities. reduced flexibility in the hamstrings is among the most commonly observed musculoskeletal issues, both in the general population and in athletes. insufficient flexibility may lead to impairments in lower extremity biomechanics, potentially resulting in various dysfunctions. loss of hamstring flexibility limits the range of motion in the knee joint and is a critical factor increasing the risk of injury. this may occur due to passive shortening from postural adaptations or active shortening caused by muscle spasm and contractions. decreased flexibility negatively affects posture, lower extremity mobility, and gait patterns. it may also lead to strength imbalances, overuse syndromes, and inefficient movement patterns. hamstring tightness can be prevented through appropriate interventions. the relative stiffness of structures such as soft tissues, joint capsules, muscles, and fascia can directly influence muscle flexibility. myofascia surrounding the muscle is a type of connective tissue that can restrict joint range of motion and reduce muscular strength and endurance in cases of inflammation, immobilization, or tissue damage. clinicians employ various manual techniques and stretching exercises to bring about therapeutic changes in these tissues, including osteopathic mobilizations, structural integration, massage, muscle energy techniques, and instrument-assisted soft tissue mobilizations. stretching exercises are one of the most common interventions used to increase hamstring flexibility. when applied regularly, these exercises have been shown to enhance muscle length and elasticity. they are also fundamental components of pre-exercise warm-up routines. dynamic stretching (ds) involves controlled movements that allow the antagonist muscle to elongate throughout its full range of motion without holding a static end position, while the agonist contracts. studies have shown that even a single session of ds can significantly improve hamstring flexibility. in individuals with hamstring tightness, ds has been found to be more effective than static stretching (ss). as an alternative, self-administered myofascial release techniques are also widely used. most commonly performed using foam rollers (fr), these techniques work similarly to traditional manual myofascial release methods. the pressure is applied with the help of body weight, providing direct and continuous pressure to the soft tissue. this pressure enhances fascial mobility, increases joint range of motion, raises fascial temperature through friction, and reduces extracellular matrix viscosity. these changes help to resolve adhesions between fascial layers and restore tissue extensibility. fr has been shown to acutely improve hamstring flexibility without negatively affecting muscle strength and may be more effective than both ss and ds exercises. peripheral muscle oxygenation refers to the level of oxygenation in muscles distant from central circulation and reflects the muscle's oxygen uptake and utilization capacity. muscle oxygenation (smo₂) measured in the hamstrings provides direct insight into the muscle's metabolic performance. recently, smo₂ measurements have become increasingly used to analyze training load, fatigue, and injury risk. however, findings on the effects of stretching or myofascial release on smo₂ remain limited. it has been suggested that both ss and ds during warm-ups may increase intramuscular oxygen availability. some studies have shown that oxygen saturation levels are higher after ds compared to ss. furthermore, combining ds or ss with fr has been shown to further increase smo₂, suggesting that the oxygen supplied exceeds the intramuscular oxygen demand. nevertheless, there is a need for studies that investigate the isolated effects of ds and fr. the aim of this study is to compare the effects of a single, isolated session of dynamic stretching and foam rolling on hamstring flexibility and peripheral muscle oxygenation. our hypothesis was that in healthy individuals with hamstring tightness, dynamic stretching would be more effective than foam rolling in increasing muscle oxygenation, while both would have similar effects on flexibility.

Eligibility criteria:
inclusion criteria: * healthy individuals aged between 18 and 35 years * both male and female participants * absence of any known health conditions * hamstring tightness defined as ≥20° of knee flexion angle in active knee extension test exclusion criteria: * any neuromuscular or orthopedic disorders affecting the lower extremities * circulatory or vascular problems * respiratory or cardiovascular diseases * renal failure * presence of pain during measurements or exercise protocols * excessive skin sensitivity or active skin infection * history of intense physical activity within the last 48 hours

Keywords: myofascial release moxy active knee extansion test warm-up near-infrared spectroscopy